1. Field of the Invention
This invention relates to an improvement of sulfonating organic compounds containing an alcoholic hydroxyl group to produce ether sulfonates useful as detergents and as surfactants for enhanced oil recovery processes.
2. Description of the Prior Art
Organic sulfonic acids and organic sulfonates are becoming increasingly important due to their use in the preparation of liquid detergents, particularly in the preparation of relatively salt-free detergents having good solubility characteristics. Even more recently, compounds of this general type have been found to be useful materials when employed as surfactants for enhanced oil recovery processes. In one general scheme sulfonated materials are prepared by sulfonation processes employing concentrated sulfuric acid or oleum. However, using such strong acids leads to the obvious problems of corrosion and/or salt disposal and separation following neutralization of the final reaction mixture to produce salt by-products. In most instances, products containing substantial amounts of the salt cannot be usefully employed, and such salt must be removed.
To obviate the above problems, another method of preparing organic sulfonates involves reacting an organic alcohol containing at least one hydroxyl group with a hydroxy-containing alkyl sulfonic acid salt. Under appropriate conditions, the two compounds are condensed with formation of by-product water to produce an ether sulfonate. A typical sulfonating (more properly sulfoalkylating) reagent here is sodium isethionate also named as the sodium salt of 2-hydroxyethane sulfonic acid.
In many instances use of hydroxy-containing alkyl sulfonic acids or salts such as 2-hydroxyethane sulfonic acid salt or other sulfonating reagents of this type involves one or more process difficulties. For example, in most instances the organic alcohol to be sulfonated and sulfonating reagent of this type are not mutually soluble one in another. As one example, the hydroxy compounds may be liquids at reaction temperatures but are not solvents for the solid, crystalline sulfonic acid salts. Hence, one is faced with a reaction system consisting of both liquid and solid phases with attendant obvious problems.
In still other instances, reactions of the above type are difficult to control or are even uncontrollable in many instances. Thus, for example, excessive foaming may occur which cannot be practically controlled or eliminated. It is important in controlling foaming to remove water by-product during the course of the reaction as such water is formed. However, resort to such well-known expedients as azeotropic distillation of said by-product water has been found to be unsuccessful or minimally useful.
In yet other processes involving the just described classes of reactants, prior art efforts were unsuccessful in that highly colored products were obtained. Yellow, brown or other colored products when used for detergent use, for example, are unsatisfactory. The discolored product requires bleaching in order to compete with like generally colorless products, which bleaching step adds considerably to the cost of production. In still other instances, sulfonation processes of this type involving the above reactants cannot be or are difficulty temperature controlled. Lastly, in some situations the proposed prior art sulfonating process cannot be adapted to batch, continuous, or semi-continuous processes, which latitude of choice is extremely desirable.
One excellent process for making ether sulfonates from hydroxy-containing sulfonic acid salts is disclosed in copending, commonly assigned Ser. No. 746,463, filed Dec. 1, 1976. This process in brief, comprises reacting said sulfonic salt with an organic alcohol under carefully controlled conditions comprising use of a vacuum measured at less than 300 mm of mercury, for at least the majority of the reaction while dispersing an inert gas through the liquid reaction mass. However, it has been noted that this process when utilizing a solid sulfonic acid salt gave rise to inhomogeneous reaction mixtures giving low product selectivities and low reaction rates. While, of course, aqueous solutions of the salt may be employed as a reactant source, this expedient does involve some drawbacks. Specifically, while working with an aqueous form of sulfonic acid salt reactant there is created the necessity of carefully metering the solution to the reaction mixture at a prescribed rate to avoid reaction difficulties. In addition, there is noted the necessity of long stripping times in order to remove water introduced. This then involves long equipment turn-around times. Additionally, there is thus noted losses of reactant by steam distillation during said stripping step. Lastly, when it is necessary to ship the sulfonic acid salt reactant to the manufacturing site in such aqueous form one must transport inert water along with the active reactant which consequently involves added shipping cost.
It is therefore a principal object of this invention to provide a process for the sulfonation of organic alcohols through reaction with solid hydroxyl-containing alkyl sulfonic acid salts, which process is free from the just-mentioned disadvantages of the prior at processes.
A specific object of the invention is to provide a method of sulfonating organic alcohols via reaction with hydroxyl-terminated lower alkyl sulfonic salts utilized in solid form such as the salt of 2-hydroxyethane sulfonic acid, which reaction can be controlled and produces the desired ether sulfonate products in relatively high yields and high product selectivities concomitant with a desired high reaction rate.
The above-mentioned objects and advantages of the present invention will become apparent as the invention is more thoroughly discussed hereinafter.